Can't eliminate vocal buzzing

I've recorded our lead singer several times over the last month, trying to eliminate a "buzzing" sound. The buzz is only present when the track is exported to a wav file, then dropped on a CD for playback. I've recorded other voices and they don't "buzz" when dropped to a CD. I've tried adjusting the gain, different mics, different effects & settings, no effects....nothing helps. I've checked to make sure the mic position is correct, and that the singer is singing over the top of the mic...not directly into it.